Chancellor Angela Merkel's rival, Peer Steinbrueck, on Sunday kicked off his bid to topple her in next year's German election, pledging social equality and a clear pro-European policy.

In a speech lasting almost two hours and punctuated with frequent bursts of enthusiastic applause, Steinbrueck said: "Freedom, justice, solidarity... with a commitment to these values, I am running to be chancellor of the Federal Republic of Germany."

"It is time for a change," thundered the 65-year-old former finance minister, rewarded with an almost 10-minute standing ovation from his Social Democratic Party (SPD) supporters in the northern city of Hanover.

With 93.45 percent of the vote, SPD delegates officially nominated Steinbrueck as their candidate for the unenviable task of unseating Merkel, often called the world's most powerful woman, at federal elections expected in September.

Steinbrueck accused Merkel's party, the conservative CDU, of having no election strategy apart from relying on her and said her political slogans were "stickers on empty bottles" with little substance behind them.

"Mrs Merkel said she is running the best and most successful government since reunification (in 1990). I have rarely laughed so much," said Steinbrueck to tumultuous applause.

He pledged to put an end to what he said was "an increasing trend toward parallel societies" in Germany, the haves and the have-nots.

While he was forced to acknowledge that Europe's economic powerhouse currently enjoyed low unemployment, he stressed that many of those in work were not being paid fairly and pledged a legal minimum hourly wage of 8.50 euros ($10.98).

On the international stage, he vowed to "show his colours and go into the federal election with a clear pro-European stance."

"Europe is more than a common market, it is more than a currency union. . . it is more than a club of 27 European leaders. Europe is civilisation," he said.

He accused Merkel of fostering "isolation" in Europe with her policies against the debt crisis.

German media had seen Steinbrueck's speech as a final chance to kick-start his campaign after damaging revelations that he had pocketed some 1.25 million euros ($1.63 million) in fees for making speeches at private functions.

This topic continued to dog him even on Sunday, as a handful of campaigners from Greenpeace briefly interrupted the speech.

Steinbrueck himself briefly touched on the issue, saying: "My fees for speeches were rocks in my backpack that you have also had to carry on your shoulders."

But commentators seemed broadly impressed with what had been billed as "the most important speech of Steinbrueck's life."

The Bild mass circulation daily said Steinbrueck was "very focused, relaxed, well very prepared."

"Steinbrueck really got into his stride, became freer, more acerbic and more self-assured, but remained statesman-like," commented Europe's most widely read paper.

Newsweekly Spiegel said Steinbrueck clearly achieved the new beginning he wanted. "Now the SPD needs some success," wrote the influential magazine in its online edition.

Opinion polls point to the scale of the task facing the centre-left SPD against Merkel, who continues to be Germany's most popular politician.

A survey released by ARD public television ahead of the party conference showed the SPD still languishing some nine points behind Merkel's conservative CDU and CSU sister party from Bavaria.

Germans do not directly elect their chancellor but if they could, 49 percent would plump for Merkel and only 39 percent would vote for Steinbrueck in the election, the poll showed, although the gap appears to be narrowing slightly.

Steinbrueck vowed he would not join with Merkel in a so-called "grand coalition" and called on party members to "trust in ourselves and others will trust in us.

"If we stand side-by-side, then we'll get there," he pledged.